Iridium wire rods are known as metallic wire rods used in such as electrodes for spark plugs (central electrodes and earth electrodes) and electrodes for various sensors. Electrodes for spark plugs are exposed to a high-temperature oxidation environment within combustion chamber, and thus, subjected to concerns about wear by high-temperature oxidation. Iridium belongs to precious metals and has high melting point and good oxidation resistance, and thus, can be used for a long term in high temperatures.
On the other hand, one that has better resistance to high-temperature oxidation is needed. As a method of improving the high-temperature oxidation resistance of an iridium wire rod, it is typical to appropriately alloy addition elements, such as rhodium, platinum, and nickel, for compositional improvement of constituent materials. Moreover, an example using a clad wire rod from combined two materials is also known recently (for example, Patent Literature 1). All of precious metals such as Pt and Ir are materials with high melting points; however, with strictly comparing, their spark wear resistances and oxidation resistances are different, and the respective advantages can be exploited using these clad materials.